JP6423265B2 - Surface coated cutting tool with excellent chipping resistance in wet high speed intermittent cutting - Google Patents

Description

  The present invention relates to a surface-coated cutting tool (hereinafter referred to as “coated tool”) that exhibits excellent chipping resistance in a hard coating layer in wet high-speed intermittent cutting such as ductile cast iron in which a high load acts on the cutting edge.

Conventionally, cutting is performed by coating a hard film made of carbide, nitride, carbonitride, or the like of at least one element selected from groups 4a, 5a, and 6a of the periodic table on the tool base surface. It is known to improve the wear resistance of tools.
Among the hard coatings, the α-type aluminum oxide layer is selected from groups 4a, 5a, and 6a in the periodic table from the viewpoints of excellent thermal stability, low reactivity, and high hardness. Further, a coated tool having an α-type aluminum oxide layer formed thereon is known as the outermost surface layer of a hard coating made of carbide, nitride, carbonitride, or the like of at least one element, but cutting conditions are severe. Accordingly, there is a need for a coated tool having cutting performance that can withstand it, and various improvements and proposals have been made for the α-type aluminum oxide layer that constitutes the outermost surface layer of the hard coating.

  For example, in Patent Document 1, at least an aluminum oxide layer is formed by a chemical vapor deposition method as a hard coating layer of a surface-coated cutting tool, and Ti oxide is dissolved or 30% by volume in the aluminum oxide layer. It has been proposed to improve the toughness, adhesion, and wear resistance of the surface-coated cutting tool by containing the following.

In Patent Document 2, a lower layer and an upper layer are formed on the surface of a tool base by chemical vapor deposition, and the lower layer includes a Ti carbide layer, a nitride layer, a carbonitride layer, a carbonate layer, and a carbonitride. The Ti compound layer composed of one or more of the oxide layers, the upper layer is an aluminum oxide layer, and the aluminum oxide layer has a columnar vertically grown aluminum oxide crystal structure, and the structure Fine aluminum oxide is dispersed and distributed therein, and the fine aluminum oxide is a granular aluminum oxide crystal phase or an amorphous aluminum oxide phase or a mixed phase of a granular aluminum oxide crystal phase and an amorphous aluminum oxide phase. The average grain width W of the crystal is 50 to 2000 nm, the average aspect ratio A is 5 to 50, and the average of the fine aluminum oxide particles is Diameter R is a 10 to 50 nm, by the number density of the cross-section of the particulate aluminum oxide is present in the aluminum oxide layer constituting the upper layer has a 20 to 150 pieces / [mu] m ^2, chipping in a high speed heavy cutting, It has been proposed to improve fracture resistance.

In Patent Document 3, in the surface-coated cutting tool, a lower layer containing at least one of ZrO ₂ , HfO ₂ , B ₂ O _3, or TiO ₂ is formed, and the size of the crystal structure is 50 nm or more and 150 nm or less thereon. 0.1 μm consisting of a mixed structure of an α-type crystal structure and a γ-type crystal structure in which the crystal grains of the α-type crystal structure are mixed at a ratio of 10% to 90%. Proposing to improve the wear resistance of surface-coated cutting tools by preventing aluminum oxide crystal grains from falling off the hard coating layer by forming an aluminum oxide film with a thickness of 10 μm or less by physical vapor deposition. Has been.

  In Patent Document 4, in a surface-coated cutting tool in which an aluminum oxide layer having an average layer thickness of 0.2 to 5 μm and high smoothness is formed on at least the outermost surface of a tool base by a sol-gel method, The aluminum layer is composed of a substrate and a spherical structure dispersed in the substrate, and the substrate is composed of an aluminum oxide crystal phase and an amorphous phase. The spherical structure is a kind of acicular crystal phase and plate-like crystal phase. Or it consists of an aggregate | assembly of 2 types and an amorphous phase, and the ratio of the area which the spherical structure | tissue which contains in the longitudinal cross-section of an aluminum oxide layer occupies 20-60 area%, and the radius of an approximate circle is 0.02-0. It has been proposed to improve the lubricity and wear resistance of the hard coating layer in high-speed heavy cutting such as cast iron and carbon steel by setting the thickness to 0.5 μm.

JP-A 61-195975 JP 2013-116548 A Japanese Patent No. 4970886 JP 2013-139076 A

  In the coated tool in which the aluminum oxide layer proposed in Patent Documents 1 and 2 is formed by chemical vapor deposition, in the cutting process under normal conditions due to the thermal stability and non-reactivity of the formed α-type aluminum oxide. It exhibits a certain degree of toughness and wear resistance, but for example, when it is used for cutting with high heat generation and intermittent and impact loads on the cutting edge, chipping and chipping are likely to occur. This has caused a problem that sufficient wear resistance cannot be exhibited over a long period of use.

  Further, in the coated tool in which the aluminum oxide layer formed by physical vapor deposition proposed in Patent Document 3 is a hard coating layer, the high-temperature stability of the aluminum oxide layer is poor and the hardness is not sufficient. There was a problem of inferiority.

Further, in the coated tool in which the aluminum oxide layer is formed by the sol-gel method proposed in Patent Document 4, the hard coating layer is made of α-Al ₂ O ₃ having excellent thermal stability and high nonreactivity. In addition, water and hydrochloric acid are added to the sol and heated to promote hydrolysis and polycondensation reactions, and a sol in which dense Al-O bonds close to α-type with a close-packed structure are dispersed is formed into a film. By using it, α-Al ₂ O ₃ having high crystallinity was formed. And when this is used for high-speed continuous cutting of cast iron / steel, it exhibits a long life, but in wet high-speed intermittent cutting of ductile iron with a large impact, the film structure is spherical or needle-like / plate-like crystals. It is composed of grains and has poor uniformity, and it is easy to cause abnormal damage such as chipping, chipping, peeling, etc. due to unevenness and cracks from the tip of needle-like crystal grains, etc. There was a problem that sufficient wear resistance could not be exhibited.

Therefore, the present inventors have conducted an intensive study to form an aluminum oxide layer excellent in chipping resistance by a sol-gel method even under cutting conditions where chipping such as intermittent cutting of ductile cast iron is likely to occur. When an aluminum oxide layer composed of α-type and γ-type mixed structures is formed by a sol-gel method using alkoxide of titanium and alkoxide of titanium as raw materials or a sol in which Ti oxide fine particles are added in advance in alumina sol The α-type aluminum oxide crystal grains formed can have a relatively large grain size and a relatively granular shape with an aspect ratio close to 1, thereby reducing the toughness of the aluminum oxide layer. It can be increased and the uniformity of the crystal grain shape is excellent. It has been found that chipping resistance and peeling resistance can be improved in combination with γ-type aluminum oxide crystal grains having excellent lubricity without causing the occurrence of the above.
And when such a coated tool coated with an aluminum oxide layer is subjected to wet high-speed intermittent cutting of ductile cast iron in which intermittent and impact loads are applied to the cutting edge, chipping, chipping, etc. may occur. It has been found that it exhibits excellent wear resistance over a long period of use.

This invention has been made based on the above findings,
“(1) An aluminum oxide layer having a mean layer thickness of 0.5 to 4.0 μm is formed as a hard coating layer on the surface of a tool base made of tungsten carbide-based cemented carbide or titanium carbonitride-based cermet. A surface-coated cutting tool comprising:
(A) The aluminum oxide layer contains a Ti oxide dispersed in the layer and has a mixed structure of α-type aluminum oxide crystal grains and γ-type aluminum oxide crystal grains,
(B) The average particle diameter of the γ-type aluminum oxide crystal grains in the aluminum oxide layer is 50 to 200 nm,
(C) The average particle diameter of the α-type aluminum oxide crystal grains in the aluminum oxide layer is 50 to 300 nm, and the average aspect ratio is 0.8 to 1.2.
(D) While the area ratio of the α-type aluminum oxide crystal grains in the longitudinal section of the aluminum oxide layer is 20 to 70%,
(E) Surface-coated cutting characterized in that the standard deviation of the area ratio occupied by α-type aluminum oxide crystal grains in each section obtained by dividing the longitudinal section of the aluminum oxide layer in parallel with the tool base surface is 15% or less. tool.
(2) The Ti content of the Ti oxide dispersed and contained in the aluminum oxide layer is 0.5 to 5 atomic% of the total metal components contained in the aluminum oxide layer ( The surface-coated cutting tool according to 1).
(3) Of the α-type aluminum oxide crystal grains formed in the aluminum oxide layer, α-type aluminum oxide crystal grains of 70 area% or more are in contact with one or more Ti oxides ( The surface-coated cutting tool according to 1) to (2).
(4) The aluminum oxide layer is formed by a sol-gel method using a sol to which Ti oxide fine particles having a particle diameter of 20 to 100 nm are added in advance. (1) to (3) The surface coating cutting tool in any one.
(5) In a surface-coated cutting tool formed by coating a hard coating layer on the surface of a tool base made of a tungsten carbide-based cemented carbide,
A base surface hardened layer having an average layer thickness of 0.5 to 3.0 μm in the depth direction from the surface of the tool base is formed, and an average content of Co as a binder phase metal contained in the base surface hardened layer is The surface-coated cutting tool according to any one of (1) to (4), which is less than 2.0% by mass.
(6) In a surface-coated cutting tool formed by coating a hard coating layer on the surface of a tool base composed of a titanium carbonitride-based cermet,
A base surface hardened layer having an average layer thickness of 0.5 to 3.0 μm in the depth direction from the surface of the tool base is formed, and the total average of Co and Ni as binder phase metals contained in the base surface hardened layer Content is less than 2.0 mass%, The surface-coated cutting tool in any one of (1) thru | or (4) characterized by the above-mentioned. "
It is characterized by.

  Hereinafter, the present invention will be described in detail.

  The coated tool of the present invention includes an aluminum oxide layer having an average layer thickness of 0.5 to 4.0 μm formed by a sol-gel method as a hard coating layer, and the average layer thickness of the layer is less than 0.5 μm. If the average layer thickness exceeds 4.0 μm, chipping is likely to occur. Therefore, the layer thickness of the aluminum oxide layer is as follows. It was determined to be 0.5 to 4.0 μm.

The aluminum oxide layer is formed as a mixed structure of α-type aluminum oxide crystal grains and γ-type aluminum oxide crystal grains in which Ti oxide is dispersedly contained in the layer.
The γ-type aluminum oxide crystal grains in the aluminum oxide layer have little effect of improving the wear resistance when the average grain size is less than 50 nm, while the average grain size exceeds 200 nm in the cutting process in which a high load acts. Since the dropout is likely to occur, the average particle diameter of the γ-type aluminum oxide crystal grains is set to 50 to 200 nm.
As for the α-type aluminum oxide crystal grains in the aluminum oxide layer, the effect of improving the wear resistance is small when the average particle diameter is less than 50 nm, while the crystal grains are used in the cutting process in which a high load acts when the average particle diameter exceeds 300 nm. Of the α-type aluminum oxide crystal grains is 50 to 300 nm.
In the present invention, the aluminum oxide layer is formed as a mixed structure of α-type aluminum oxide crystal grains and γ-type aluminum oxide crystal grains, and the starting point of cracks due to the uniformity of γ-type aluminum oxide having excellent lubricity and the crystal grain shape. There is no brittle part such as the tip of the crystal grains that become, and it has a layer structure that combines α-type aluminum oxide with excellent high-temperature hardness and oxidation resistance, so that it is the starting point of delamination that is feared when laminated Since there is no formation of a fragile layer, even under intermittent cutting conditions in which a high load acts on the cutting edge, the occurrence of chipping, peeling, etc. is suppressed, and excellent cutting performance is demonstrated over a long period of use.

The α-type aluminum oxide has high-temperature hardness and oxidation resistance, but the average aspect ratio of the α-type aluminum oxide crystal grains is set to 0.8 to 1.2 to form granular crystals, Even in high-speed intermittent cutting of ductile cast iron subjected to a large impact, the crystal grain shape is excellent in uniformity, so that cracks do not occur from fragile parts such as the tip of the crystal grain, resulting in chipping resistance and peeling resistance. Can be further improved.
Here, when the average aspect ratio of the α-type aluminum oxide crystal grains is less than 0.8 and exceeds 1.2, the α-type oxidation is provided with high temperature hardness and oxidation resistance and mainly responsible for wear resistance of the aluminum oxide layer. Α-type aluminum oxide crystal grains are less prone to drop-off chipping due to the non-uniformity of the aluminum crystal grains and the occurrence of cracks from the non-uniformity and the tips of needle-like grains. The average aspect ratio is set to 0.8 to 1.2.
The average aspect ratio refers to, for example, the α-type aluminum oxide crystal grains in the aluminum oxide layer in cross-sectional observation using a scanning electron microscope (5000 times magnification) equipped with an electron beam backscattering diffractometer (EBSD). The particle width w and the particle length l of the α-type aluminum oxide crystal grains are measured, and α-type aluminum oxide crystal grains existing in the range of a total length of 10 μm in the horizontal direction with respect to the tool base are measured. The aspect ratio L / W defined as the ratio of the average particle width W, which is the average value of the particle widths w obtained with respect to, and the average particle length L, which is the average value of the particle length l, obtained for each crystal grain. It can be obtained as an average aspect ratio.

In the present invention, the average occupation area ratio of the α-type aluminum oxide crystal grains in the longitudinal section of the aluminum oxide layer is in the range of 20 area% to 70 area%.
This is because when the occupied area ratio of the α-type aluminum oxide crystal grains is less than 20 area% in the measurement cross section, the effect of improving the wear resistance is small, whereas when the occupied area ratio exceeds 70 area%, the lubricity is increased. This is because the amount of the γ-type aluminum oxide crystal grains excellent in the reduction in the number of particles is reduced.
Further, when the standard deviation of the occupied area ratio of α-type aluminum oxide crystal grains is calculated for each section of the aluminum oxide layer sectioned parallel to the tool base surface, the layer thickness direction of the aluminum oxide layer is 15 area% or less. The distribution of the area ratio of the α-type aluminum oxide crystal grains and the area ratio of the γ-type aluminum oxide crystal grains is almost uniform, so that the aluminum oxide of the present invention has lubricity, crack resistance, high temperature hardness, and oxidation resistance. It is further desirable because the characteristics of the layer are uniformly ensured over the thickness direction of the aluminum oxide layer, and the above effects can be exhibited over a long period of time.
In addition, the area ratio of the α-type aluminum oxide crystal grains in each cross section of the aluminum oxide layer divided in parallel with the tool base surface is determined by dividing the aluminum oxide layer by 0.2 μm in height in the layer thickness direction, for example. The measured cross section can be obtained by measuring the area ratio of α-type aluminum oxide crystal grains.

In the present invention, the Ti oxide is dispersed and contained in the aluminum oxide layer. The Ti oxide dispersed and contained in the layer is α-type oxidized when the aluminum oxide layer is formed by the sol-gel method. It becomes a nucleation point of aluminum crystal grains and promotes refinement of α-type aluminum oxide crystal grains, and at the same time contributes to improvement of toughness of the aluminum oxide layer.
When the content ratio of Ti oxide dispersed and contained in the aluminum oxide layer is converted to Ti amount relative to all metal components contained in the aluminum oxide layer, when the Ti content is less than 0.5 atomic%, α There is little effect of refining type aluminum oxide crystal grains, and an aluminum oxide layer having a uniform structure cannot be formed. On the other hand, if the Ti content exceeds 5 atomic%, the hardness of the aluminum oxide layer decreases, The content ratio of the Ti oxide is preferably 0.5 to 5 atomic% in terms of the amount of Ti with respect to all metal components contained in the aluminum oxide layer.
The content ratio of Ti in the total metal elements in the aluminum oxide layer is, for example, the energy dispersive X attached to the TEM for the longitudinal sectional view region (for example, a range of 0.2 μm × 0.3 μm) of the aluminum oxide layer. The measurement can be performed by performing quantitative visual field analysis within the observation visual field range by a line analyzer and obtaining an average value thereof.
In order to set the Ti content in the aluminum oxide layer to 0.5 to 5 atomic%, a sol in which a predetermined amount of titanium alkoxide is simultaneously used as a raw material or a predetermined amount of Ti oxide fine particles are added in advance is used. An aluminum oxide layer can be formed by the sol-gel method used. In this case, it is desirable to use TiO ₂ fine particles having a particle size of 20 to 100 nm as the Ti oxide fine particles, and also an alkoxide of titanium or Ti oxide. The addition amount of the fine particles is preferably 0.005 mol% to 0.05 mol% as the addition amount with respect to the solid content of the alumina sol.

In the present invention, since the fine Ti oxide acts as a load buffer so as to fill the periphery of the α-type aluminum oxide crystal grains, particularly under cutting conditions in which a high load acts, around the α-type aluminum oxide crystal grains, It is preferable that one or more Ti oxide crystal grains are dispersedly contained so as to be in contact with each other. Of the area occupied by the α-type aluminum oxide crystal grains in the observation visual field range, the area occupied by the α-type aluminum oxide crystal grains formed in contact with the Ti oxide around the α-type aluminum oxide crystal grains is less than 70%. However, the load at the time of cutting cannot be relieved, the α-type aluminum oxide crystal grains are likely to fall off, and the toughness improving effect of the aluminum oxide layer is reduced.
Whether or not one or more Ti oxide crystal grains are present around the α-type aluminum oxide crystal grains is determined using, for example, an electron beam backscattering diffraction device (EBSD) and an Auger electron spectroscopy device (AES). Can be confirmed. First, the position of the α-type aluminum oxide crystal grains observed in the observation field range of layer thickness × 10 μm was specified by EBSD, and then the observation range was specified by EBSD using an Auger electron spectrometer. When elemental analysis around the α-type aluminum oxide crystal grains is performed, it can be confirmed whether or not one or more Ti oxide crystal grains are formed around the α-type aluminum oxide crystal grains.

The aluminum oxide main layer can exhibit its performance by directly forming a film on the tool base. However, when a cemented carbide containing titanium carbonitride is used as the base, it can be used in a nitrogen atmosphere. By firing, a large amount of at least one kind of highly wear-resistant carbonitride of Ti, Ta, Nb, and Zr is contained in the vicinity of the tool base surface to form a base surface hardened layer, and an aluminum oxide main layer and The adhesion strength with the tool base can be improved and the tool life can be extended. In addition, it is preferable that the hardness of the cemented carbide base body after this base-surface hardened layer formation is 2200 or more and 2800 or less in terms of Vickers hardness (Hv). At that time, Co in the vicinity of the substrate surface is relatively reduced by containing a large amount of carbonitride, and for example, 0.5 to 3.0 μm in the depth direction from the surface using a scanning electron microscope (SEM). When the content of Co as a binder phase metal is detected by quantitative analysis by wavelength dispersive X-ray spectroscopy in an analysis visual field range of 1 × 1 μm, the Co content is 2. If it is less than 0% by mass, carbonitrides that cause surface hardening of the substrate are sufficiently formed, and wear resistance is further improved.
If the average thickness of the substrate surface hardened layer is 0.5 μm or less, it will be worn away relatively quickly without exhibiting sufficient wear resistance, and if it is 3.0 μm or more, chipping is likely to occur.

  In addition, when the titanium carbonitride-based cermet is used as a substrate, the atmosphere when holding at the highest temperature and the highest temperature in the sintering process is a predetermined nitrogen atmosphere, and by reducing the pressure during holding or when lowering the temperature, The surface can be cured more than when the entire sintering process is performed in a nitrogen atmosphere at a constant pressure. This is because when the process up to holding at the maximum temperature is performed under a constant nitrogen pressure, carbonitrides with high hardness are uniformly dispersed inside the substrate. Is treated under a relatively high nitrogen pressure, and during treatment or when the temperature is lowered to a more reduced nitrogen atmosphere, only the very surface of the substrate is denitrified, resulting in a Ni or Co metal bonded phase. This is because dissolution of Ti and Nb and diffusion from the inside to the surface of the substrate become active, formation of carbonitrides such as Ti and Nb is promoted on the surface, and a substrate surface hardened layer is formed. In addition, it is preferable that the hardness of the cermet base | substrate after this base-surface hardened layer formation is 2000 or more and 2600 or less in Vickers hardness (Hv). In this case, similarly to the above-mentioned carbide substrate, Ni and Co in the vicinity of the substrate surface are relatively reduced. For example, 0.5 to 0.5 in the depth direction from the surface using a scanning electron microscope (SEM). When the cross section of 3.0 μm is observed and quantitative analysis is performed by wavelength dispersive X-ray spectroscopy in the analysis visual field region range of 1 × 1 μm, the total content of Ni and Co as binder phase metals is 2.0 mass. If it is less than%, carbonitrides that cause surface hardening of the substrate are sufficiently formed, and wear resistance is further improved.

The α-type aluminum oxide layer constituting the surface layer of the coated tool of the present invention can be formed, for example, by the sol-gel method shown below.
In the present invention, when the α-type aluminum oxide layer is formed by the sol-gel method, mainly the sol-gel method using titanium alkoxide at the same time as the aluminum alkoxide as the raw material, or Ti oxidation to alumina sol. The sol-gel method for adding fine particles can be used, and the above two methods will be mainly described. The Ti oxide fine particles are added by a surface treatment that allows uniform dispersion in alumina sol. There are various methods such as a method of adding oxide fine particles, a method of adding Ti oxide fine particles uniformly in alcohol, a method of adding a dispersant to alumina sol and then adding Ti oxide fine particles to alumina sol. Although it is possible, any addition method may be used.

In general, high temperature of 1000 ° C. or higher is required for crystallization of aluminum oxide, in particular, α conversion, but Ti oxide contributes to the crystallization promotion of aluminum oxide. Crystallization becomes possible at low temperature. The mechanism of the low-temperature crystallization accelerating effect of aluminum oxide by Ti oxide is not clearly elucidated, but considering the standard free energy of formation of various metal oxides, Ti oxide is thermodynamically more than Al oxide. Ti oxides can oxidize Al elements, that is, Ti oxides are considered to be an oxygen supply source for oxidizing Al by reduction, and more than one metal oxide Of these, Ti is the metal element closest to the standard free energy of formation of Al, and therefore Ti oxide is considered to be particularly effective in promoting crystallization of aluminum oxide. As is known in the manufacturing method, it is relatively low temperature that cannot normally be obtained through the sol state and gel state due to the network formation of metal element and O Considering that this is a technique that can achieve crystallization with the oxygen supply of Ti oxide, the formation of Al and O networks may be promoted at a relatively low temperature stage. It becomes a starting point for growth of aluminum oxide crystal grains, and crystallization is possible at a relatively low temperature in a limited portion near the Ti oxide.
However, when the average particle diameter of the Ti oxide fine particles added to the alumina sol is less than 20 nm, the supply of oxygen necessary for oxidizing aluminum is not sufficient, so that it is difficult to crystallize, and when the average particle diameter exceeds 100 nm, Coarse Ti oxide is contained in the aluminum oxide layer, and after firing, it tends to be a starting point for cracks and peeling. Therefore, the average particle diameter of the Ti oxide fine particles added to the alumina sol is preferably 20 to 100 nm.

Preparation of alumina sol:
First, when performing a sol-gel process using titanium alkoxide, aluminum alkoxide (eg, aluminum secondary butoxide, aluminum isopropoxide), titanium alkoxide (eg, titanium isopropoxide, titanium ethoxide, etc.) and alcohol (E.g., ethanol, propanol), followed by acid (e.g., hydrochloric acid, nitric acid), and then gradually proceeding to the hydrolysis reaction to form a precursor densely, the temperature range below 10C Alumina sol is prepared by stirring for 12 hours or longer. In the usual preparation of alumina sol, stirring at 40 to 80 ° C. and aging treatment for about several hours is performed at the stirring temperature. In the present invention, stirring in a low temperature range of −10 to 10 ° C. It is desirable to perform low-temperature treatment over a long period of time, for example, for a total of 12 hours or more.
This is because when the temperature during stirring and aging treatment exceeds 10 ° C., the hydrolysis and polycondensation reaction proceed rapidly, so that the aluminum oxide precursor is difficult to be formed densely, and the α-type is formed in the subsequent baking treatment. Since it is difficult to form aluminum oxide, the upper limit of the temperature at the time of stirring and aging treatment is 10 ° C. On the other hand, when the temperature at the time of stirring and aging treatment is less than -10 ° C, hydrolysis and polycondensation reaction hardly proceed, This is because it becomes difficult to crystallize.
In addition, the stirring and aging time was set to 12 hours or more in total so that the chemical reaction occurring in the temperature range during the stirring and aging was sufficiently brought to an equilibrium state, and the network of hydrolytic polycondensation Al and O was dense. This is the time required to obtain the formed stable aluminum oxide precursor sol.

  The concentration of the acid to be added is preferably 0.01 to 1.0 N, and the amount of acid added to the alcohol is preferably 0.1 to 2 times (volume).

Heat treatment of alumina sol:
Next, the alumina sol is heated and stirred for 6 hours or more for the purpose of proceeding until the hydrolysis / condensation reaction occurring in the sol reaches an equilibrium state. In addition, it is desirable to use a reflux heat treatment such as an oil bath used in general organic synthesis as the heat treatment, and it is desirable to perform the heat treatment at a temperature of 80 to 180 ° C. depending on the components of the sol. .
In addition, when the sol-gel method of adding Ti oxide fine particles to alumina sol without using titanium alkoxide, after stirring in a temperature range of −10 to 10 ° C. or in a temperature range of 80 to 180 ° C. It is desirable to add Ti oxide fine particles after the heating and stirring in step (b).

Drying and firing:
A tool base coated with a tool base or an underlayer (for example, a Ti compound layer) is immersed in the alumina sol prepared above, and then pulled up from the alumina sol at a rate of 0.5 mm / sec. A drying treatment is performed at ˜600 ° C. for 10 minutes, this immersion treatment and the drying treatment are repeated until the required layer thickness is obtained, and then a baking treatment is carried out in a temperature range of 700 to 900 ° C.

  By the drying treatment, a dry gel of alumina containing finely divided Ti oxide is formed, and then by a firing treatment to be performed, a predetermined amount (0.5 to 5 atomic% of all metal elements) is added in the aluminum oxide phase. An aluminum oxide layer composed of a mixed structure of α-type aluminum oxide crystal grains and γ-type aluminum oxide crystal grains containing finely divided Ti oxide is dispersed.

  The film thickness of the aluminum oxide layer depends on the number of immersions in the alumina sol, but if the average layer thickness of the coated aluminum oxide layer is less than 0.5 μm, it has excellent wear resistance as a coated tool over a long period of use. On the other hand, if the average layer thickness exceeds 4.0 μm, the aluminum oxide layer tends to be peeled off. Therefore, the thickness of the aluminum oxide layer is set to 0.5 to 4.0 μm.

In addition, when the firing temperature is less than 700 ° C., α-type aluminum oxide crystal grains having a predetermined area ratio are formed because the formation rate of α-type aluminum oxide crystal grains is slow even if titanium alkoxide or Ti oxide fine particles are used. It is not possible to form an aluminum oxide layer having sufficient high temperature hardness with high crack resistance and effective in wet high-speed intermittent cutting. On the other hand, when fired at a temperature exceeding 900 ° C., γ-type aluminum oxide crystal grains having a predetermined area ratio cannot be formed, so that the lubricity of the aluminum oxide layer is lowered, and excellent chipping resistance and chipping resistance are obtained in wet high-speed intermittent cutting. I can't show my sexuality.
Therefore, the firing temperature is desirably 700 to 900 ° C.

  According to the surface-coated cutting tool of the present invention, a film is formed on the surface of the tool base by a sol-gel method in which titanium alkoxide is added to a raw material or a sol-gel method using a sol in which Ti oxide fine particles are added in advance. Covers and forms an aluminum oxide layer consisting of a mixed structure of α-type aluminum crystal grains and γ-type aluminum oxide crystal grains containing a dispersed Ti oxide, and has the lubricity of γ-type aluminum oxide and α-type aluminum oxide. It has a layer structure that combines excellent high-temperature hardness and oxidation resistance, and the toughness of the layer is improved by the Ti oxide dispersed and contained in the aluminum oxide layer. Even in wet high-speed intermittent cutting of ductile cast iron that acts on the load, the occurrence of abnormal damage such as chipping and peeling is suppressed, and it can be used for a long time. Than is to exert excellent cutting performance Te.

  Next, the present invention will be specifically described with reference to examples.

(A) As a raw material powder, fine WC powder having an average particle diameter of 0.8 μm, medium WC powder having an average particle diameter of 2 to 3 μm, and TiCN powder, ZrC powder, TaC powder each having an average particle diameter of 1 to 3 μm, After preparing NbC powder, Cr ₃ C ₂ powder and Co powder, these raw material powders were blended in the prescribed blending composition shown in Table 1, added with wax, ball mill mixed in acetone for 24 hours, and dried under reduced pressure , Pressed into a green compact of a predetermined shape at a pressure of 98 MPa, this green compact was vacuum-sintered at a temperature of 1400 ° C. for 1 hour in a vacuum of 5 Pa, and after sintering, the cutting edge portion R: A tool base A, B, C, D, E, F, G, H, I made of WC base cemented carbide having an insert shape specified in ISO / CNMG120408 by honing to 0.05 mm. (Tool substrate A, It was prepared C, D, E, F, G, H, a) that I.
However, after holding at 1400 ° C. for 1 hour, cooling to 1320 ° C. is performed for 40 minutes in a nitrogen atmosphere of 3.3 kPa for the carbide substrate F, and in a nitrogen atmosphere of 1 kPa for the carbide substrate G. The substrate surface is cured by cooling for 40 minutes in a nitrogen atmosphere of 2 kPa for carbide substrate H and for 120 minutes in a nitrogen atmosphere of 3.3 kPa for carbide substrate I. did.

(B) Next, a lower layer was formed on the tool bases A to I.
In forming the lower layer, the tool bases A and B are charged into a chemical vapor deposition apparatus, and the TiN layer, TiCN layer, TiCO layer, TiCNO having a granular crystal structure are formed using the film formation conditions shown in Table 2. An underlayer was formed in advance with a Ti compound layer comprising a layer and a TiCN layer having a vertically grown crystal structure (hereinafter referred to as 1-TiCN) with a film configuration shown in Table 5. On the other hand, the tool base C is inserted into an arc ion plating apparatus which is a kind of physical vapor deposition apparatus, and an underlayer composed of Ti _0.5 Al _0.5 N layers having the film thicknesses shown in Table 5 is formed in advance. did.
Further, the tool base D was similarly inserted into an arc ion plating apparatus, and an underlayer composed of an Al _0.7 Cr _0.3 N layer having a thickness shown in Table 5 was formed in advance.
On the other hand, for the tool bases E, F, G, H, and I, the base layer was not particularly formed.

(C) On the other hand, an alumina sol for coating the aluminum oxide layer by the sol-gel method was prepared as follows.
After adding titanium isopropoxide, which is an alkoxide of titanium, and a predetermined amount of ethanol, which is also shown in Table 3, to aluminum secondary butoxide, which is a predetermined amount of aluminum alkoxide shown in Table 3, the mixture is stirred at 10 ° C. or less in a thermostatic bath. Furthermore, hydrochloric acid to which a predetermined amount of water was added was added dropwise over 1 to 3 hours.

(D) A predetermined amount of Ti shown in Table 3 after stirring and heating for a predetermined time for the purpose of stabilizing the hydrolysis / condensation polymerization reaction in the sol at a temperature shown in Table 3 using a reflux apparatus using an oil bath. An alumina sol was prepared by adding fine oxide particles.
The final solution composition is in molar ratio
(Aluminum secondary butoxide): (water): (ethanol): (hydrochloric acid)
= 1: (80 to 120): 20: (0.1 to 1)
Adjustments were made to

(E) Next, the tool bases A to I are immersed in the alumina sol, and then the tool bases A to I are pulled up from the alumina sol at a lifting speed of 0.5 mm / sec and dried at 500 ° C. for 10 minutes. And, after repeating dipping, pulling up and drying treatments, firing treatment was performed under the conditions shown in Table 3, and the aluminum oxide of the present invention comprising a mixed structure of α-type aluminum oxide crystal grains and γ-type aluminum oxide crystal grains By coating the layers, the coated tools 1 to 15 of the present invention shown in Tables 5 and 6 (referred to as the present tools 1 to 15) were produced.

  When the average layer thickness of the aluminum oxide layer was measured using a transmission electron microscope for the tools 1 to 15 of the present invention, the average value was substantially the same as the target layer thickness (average value of five locations). .

  Moreover, about the aluminum oxide layer of the said invention tools 1-15, when each crystal grain was analyzed by the limited visual field electron diffraction method using the X-ray-diffraction apparatus and the transmission electron microscope (TEM), from the crystal grain, A clear electron diffraction pattern was obtained, and the analysis of the pattern and the X-ray diffraction pattern confirmed that the aluminum oxide layer had a mixed structure of α-type aluminum oxide crystal grains and γ-type aluminum oxide crystal grains. It was.

  In addition, Ti oxide was dispersed and contained in the aluminum oxide layer, and the content of Ti contained as Ti oxide was measured with an energy dispersive X-ray analyzer by TEM.

Furthermore, in the aluminum oxide layer, the α-type aluminum oxide crystal grains and the γ-type aluminum oxide crystal grains, the aspect ratio of the α-type aluminum oxide crystal grains, and the α-type occupied in the aluminum oxide layer in the longitudinal section of the aluminum oxide layer The area occupied by aluminum oxide crystal grains and the area of α-type aluminum oxide crystal grains in contact with one or more Ti oxides were measured using an electron beam backscattering diffractometer (EBSD) and an Auger electron spectrometer (AES). From the measurement results, the standard deviation of the area ratio occupied by the α-type aluminum oxide crystal grains in each cross section divided in parallel with the substrate surface at every 0.2 μm height in the layer thickness direction was calculated.
The measurement method for each is as follows.
First, when the longitudinal section of the aluminum oxide layer is observed with an electron beam backscattering diffractometer (EBSD) in the observation field range of layer thickness × 10 μm, α-type aluminum oxide crystal grains and γ-type aluminum oxide crystal grain shapes can be confirmed. When the respective crystal grain shapes within the observation visual field range are obtained with respect to five visual fields, the maximum diameter in the layer thickness vertical direction is the grain size in the layer thickness vertical direction, and the maximum diameter in the layer thickness direction is in the layer thickness direction. It is defined as the particle size, and the average thereof is defined as the average particle size of α-type aluminum oxide crystal grains or γ-type aluminum oxide crystal grains. Further, the ratio of the grain size in the layer thickness direction to the grain size in the layer thickness vertical direction is calculated, and the average value is defined as the average aspect ratio of the crystal grains in the aluminum oxide layer. Further, the α-type aluminum oxide crystal grains formed in the aluminum oxide layer specified by the electron beam backscattering diffractometer (EBSD) are specified, and the area of the α-type aluminum oxide crystal grains in the aluminum oxide layer is determined. In addition, each section is sectioned at a height of 0.2 μm in the layer thickness direction, the area ratio of α-type aluminum oxide crystal grains in the aluminum oxide layer for each section is obtained, and the standard deviation over the entire longitudinal section is obtained. Asked. Further, among the α-type aluminum oxide crystal grains formed in the aluminum oxide layer by an Auger electron spectrometer (AES), α-type aluminum oxide crystal grains that are in contact with one or more Ti oxides are identified, and the area ratio thereof Asked.

[Comparative Example 1]
For comparison, a coated tool of a comparative example was manufactured by the following manufacturing method.

(A) First, the solution composition of each component in the reaction raw material is a molar ratio,
(Aluminum secondary butoxide): (water): (ethanol): (hydrochloric acid)
= 1: (80 to 120): 20: (0.1 to 1)
The alumina sol was prepared under the conditions shown in Table 4.
(B) Next, the alumina sol was applied to the surfaces of the tool bases A to I.
(C) Next, the coated alumina sol is dried under the conditions shown in Table 4, and after repeating the coating and drying until a predetermined layer thickness is obtained, the firing treatment is performed, and the results are shown in Tables 5 and 7. Comparative tools 1 to 15 (referred to as comparative tools 1 to 15) were produced.

  About Comparative example tools 1-15, when the cross-sectional measurement was carried out using the transmission electron microscope for the average layer thickness of the aluminum oxide layer, all showed the average value (average value of five places) substantially the same as target layer thickness.

  Moreover, about the aluminum oxide layer of the comparative example tools 1-15, each X-ray diffraction apparatus and a transmission electron microscope (TEM) are used, The each crystal grain is analyzed by a limited field electron diffraction method, The electron from the crystal grain The crystal structure of the aluminum oxide layer was specified from the line diffraction pattern and the X-ray diffraction pattern.

  Further, in the same manner as in Example 1, the state in which the Ti oxide was dispersedly contained in the aluminum oxide layer was measured, and the content of Ti contained as the Ti oxide was measured.

Further, the α-type aluminum oxide crystal grains of the α-type aluminum oxide crystal grains and the γ-type aluminum oxide crystal grains of the aluminum oxide layer, the aspect ratio of the α-type aluminum oxide crystal grains, and the α-type aluminum oxide crystal grains occupied in the tool base surface and the aluminum oxide layer And the area of α-type aluminum oxide crystal grains in contact with one or more Ti oxides were measured using an electron beam backscattering diffractometer (EBSD) and an Auger electron spectrometer (AES). Also, from the measurement results, the standard deviation over the entire longitudinal section was calculated from the area ratio occupied by the α-type aluminum oxide crystal grains in each section divided in parallel with the tool base surface for every 0.2 μm height in the layer thickness direction. .
The measurement method for each is the same as in Example 1.

Next, the present invention tools 1 to 15 and comparative tools 1 to 15 were subjected to the following wet high-speed intermittent cutting test of ductile cast iron, and all measured the flank wear width of the cutting edge.
Work material: JIS / FCD700 lengthwise equal length 4 round bar with round groove,
Cutting speed: 220 m / min,
Cutting depth: 1.0 mm,
Feed: 0.2mm / rev,
Cutting time: 7 minutes
(Normal cutting speed is 180 m / min),
These results are shown in Table 8.

TiCN (mass ratio TiC / TiN = 50/50) powder, Mo ₂ C powder, NbC powder, TaC powder, WC powder, Co powder, and raw material powder, all having an average particle diameter of 0.5 to 2 μm, and Ni powders were prepared, blended into the prescribed composition shown in Table 9, wet mixed for 24 hours with a ball mill, dried, and then pressed into a green compact at a pressure of 98 MPa. Sintered in a nitrogen atmosphere of 3 kPa at a temperature of 1540 ° C. for 1 hour, and after sintering, the cutting edge part is subjected to a honing process of R: 0.07 mm to form an ISO standard / CNMG120408 chip shape. TiCN based cermet tool bases J, K, L, M, N, O, P, Q, and R (referred to as tool bases J to R) were manufactured. However, for the tool base O, in a nitrogen atmosphere of 1.3 kPa, the rate of temperature rise was 2 ° C./min, the temperature was raised from room temperature to 1540 ° C. and held for 30 minutes, then a vacuum of 13 Pa was applied, and further at 1540 ° C. After holding for 30 minutes, the temperature was lowered to cure the surface. For the tool base P, the temperature was always increased and held at 1540 ° C. for 60 minutes in a vacuum of 13 Pa. For the tool base Q, the temperature was raised from room temperature to 1540 ° C. in a nitrogen atmosphere of 1.3 kPa for 30 minutes. , A vacuum of 13 Pa, and further held at 1540 ° C. for 5 minutes, and the tool substrate R was heated from room temperature to 1540 ° C. in a nitrogen atmosphere of 1.3 kPa and held for 30 minutes, and then a vacuum of 13 Pa was further obtained. After holding at 1540 ° C. for 90 minutes, the temperature was lowered to cure the surface.

  Next, an aluminum oxide layer was formed on the tool bases J to R using the underlayer deposition conditions shown in Table 2, the preparation conditions and the firing conditions shown in Table 3, as in Example 1. Table 10 The coated tools 16 to 30 of the present invention (referred to as the present invention tools 16 to 30) shown in FIG.

[Comparative Example 2]
Using the same tool bases J to R used in Example 2, the sol-gel method was used to form the underlayer shown in Table 2 and the sol preparation conditions shown in Table 3 as in Example 2. Then, the aluminum oxide main layer was formed using firing conditions until the predetermined target layer thickness shown in Table 12 was reached, and the coated tools 16 to 30 (referred to as Comparative Tools 16 to 30) of Comparative Examples shown in Tables 10 and 12 were used. Manufactured.

For the aluminum oxide layers of the inventive tools 16-30 and comparative tools 16-30, the average layer thickness of the aluminum oxide layer, the crystal structure of the aluminum oxide layer, and the dispersion of Ti oxide are the same as in Example 1. State, Ti content, grain size of each crystal grain, aspect ratio, ratio of area occupied by α-type aluminum oxide crystal grains in the aluminum oxide layer, parallel to the tool substrate surface every 0.2 μm height in the layer thickness direction From the area ratio occupied by α-type aluminum oxide crystal grains in each of the vertical sections, the standard deviation and the area ratio of α-type aluminum oxide crystal grains in contact with one or more Ti oxides were measured.
Tables 11 and 12 show the results.

About the said this invention tools 16-30 and comparative example tools 16-30, the wet high-speed intermittent cutting test was done on the following conditions.
Work material: JIS / FCD450 lengthwise equidistant round bars with 4 vertical grooves,
Cutting speed: 330 m / min,
Cutting depth: 1.3 mm,
Feed: 0.18mm / rev,
Cutting time: 7 minutes
(Normal cutting speed is 300 m / min),
These results are shown in Table 13.

  From the results shown in Tables 8 and 13, in the tools 1 to 30 of the present invention, the surface of the tool base is coated with an aluminum oxide layer containing Ti oxide dispersed by a sol-gel method. It consists of a mixed structure of α-type aluminum oxide crystal grains with excellent high-temperature hardness and oxidation resistance and γ-type aluminum oxide crystal grains with excellent crack resistance, and further, Ti oxidation in the aluminum oxide layer Since the toughness of the layer is improved depending on the object, even when this is used for wet high-speed intermittent cutting such as ductile cast iron, it does not cause abnormal damage such as chipping and peeling, and it can be used for a long time. It exhibits excellent cutting performance.

On the other hand, comparative tools 1 to 30 reach the service life in a short time due to occurrence of abnormal damage such as chipping and peeling or insufficient wear resistance in wet high-speed intermittent cutting of steel, cast iron and the like. It is clear.
In the above-described embodiment, the performance of the hard coating layer was evaluated using an insert-shaped tool, but it goes without saying that the same result can be obtained with a drill, an end mill, or the like.

  According to the surface-coated cutting tool of the present invention, an aluminum oxide layer is formed on the surface by a sol-gel method, and the aluminum oxide layer has excellent crack resistance, high temperature hardness, oxidation resistance, and toughness. Therefore, even when this is used for wet high-speed intermittent cutting such as ductile cast iron, it exhibits excellent cutting performance over a long period of use without causing abnormal damage such as chipping and peeling, The tool life can be extended, and its practical effect is great.

Claims (6)

Surface coated cutting formed by coating an aluminum oxide layer with an average layer thickness of 0.5 to 4.0 μm as a hard coating layer on the surface of a tool base made of tungsten carbide based cemented carbide or titanium carbonitride based cermet A tool,
(A) The aluminum oxide layer contains a Ti oxide dispersed in the layer and has a mixed structure of α-type aluminum oxide crystal grains and γ-type aluminum oxide crystal grains,
(B) The average particle diameter of the γ-type aluminum oxide crystal grains in the aluminum oxide layer is 50 to 200 nm,
(C) The average particle diameter of the α-type aluminum oxide crystal grains in the aluminum oxide layer is 50 to 300 nm, and the average aspect ratio is 0.8 to 1.2.
(D) While the area ratio of the α-type aluminum oxide crystal grains in the longitudinal section of the aluminum oxide layer is 20 to 70%,
(E) Surface-coated cutting characterized in that the standard deviation of the area ratio occupied by α-type aluminum oxide crystal grains in each section obtained by dividing the longitudinal section of the aluminum oxide layer in parallel with the tool base surface is 15% or less. tool.   The Ti content of the Ti oxide dispersed and contained in the aluminum oxide layer is 0.5 to 5 atomic% of the total metal components contained in the aluminum oxide layer. The surface-coated cutting tool described. 3. The α-type aluminum oxide crystal grains formed in the aluminum oxide layer, wherein 70% by area or more of α-type aluminum oxide crystal grains are in contact with one or more Ti oxides. The surface-coated cutting tool according to claim 1.   4. The aluminum oxide layer according to claim 1, wherein the aluminum oxide layer is formed by a sol-gel method using a sol to which Ti oxide fine particles having a particle diameter of 20 to 100 nm are added in advance. 5. The surface-coated cutting tool described. In a surface-coated cutting tool formed by coating a hard coating layer on the surface of a tool substrate made of a tungsten carbide-based cemented carbide,
A base surface hardened layer having an average layer thickness of 0.5 to 3.0 μm in the depth direction from the surface of the tool base is formed, and an average content of Co as a binder phase metal contained in the base surface hardened layer is The surface-coated cutting tool according to claim 1, wherein the surface-coated cutting tool is less than 2.0% by mass. In a surface-coated cutting tool formed by coating a hard coating layer on the surface of a tool base made of titanium carbonitride-based cermet,
A base surface hardened layer having an average layer thickness of 0.5 to 3.0 μm in the depth direction from the surface of the tool base is formed, and the total average of Co and Ni as binder phase metals contained in the base surface hardened layer Content is less than 2.0 mass%, The surface-coated cutting tool as described in any one of Claims 1 thru | or 4 characterized by the above-mentioned.